The present invention relates generally to fiber reinforced tubular elements such as vehicle drive shafts and, in particular, to a graphite reinforced aluminum drive shaft and a method for producing such a drive shaft.
Over the past decade, there has been an ongoing endeavor by the industry to reduce the weight of vehicles in order to improve fuel economy. In addition to downsizing and redesigning vehicles to make the most efficient use of the available space, a great deal of attention has been given to constructing various vehicular components of lighter weight materials. For example, in the area of drive shafts, it has been proposed to replace conventional steel drive shafts with lighter weight aluminum tubes. However, depending on the length of the drive shaft, and the maximum speed at which the drive shaft is to be rotated, vibration problems can arise.
While typically the tubular steel or aluminum drive shafts are adequate to transmit the torsional forces involved, there is a tendency for a shaft to "whip" or resonate mechanically when the shaft reaches a certain vehicle speed, typically referred to as a critical speed. Consequently, in order to overcome the critical speed limitations of single long drive shafts, typically multiple sections of shafts are employed. In these instances, adjacent individual drive shaft sections are connected to one another by means of a universal joint assembly which in turn is supported by a bearing mounting unit affixed to the vehicle frame.
In order to accommodate a longer drive shaft such that the universal joint assemblies and the bearing mounting units can be eliminated, it has been proposed to reinforce metal tubes with a fiber reinforced sleeve portion to increase the axial stiffness of the shaft without substantially increasing its weight. For example, U.S. Pat. Nos. 4,131,701; 4,173,670; and 4,214,932 all disclose fiber composite aluminum drive shafts wherein aluminum tubes are wrapped with alternating layers of resin-impregnated woven fiberglass cloth and resin-impregnated fiber reinforcing sheets. The reinforcing sheets are comprised of continuous unindirectional graphite fiber layers, with the graphite fibers arranged at angles between .+-.5.degree. to .+-.20.degree. with respect to the longitudinal axis of the tube. Another approach to reinforcing a tubular metallic drive shaft is disclosed in U.S. Pat. No. 4,272,971, which discloses a drive shaft wherein the fiber reinforcing layer is applied to the inside surface of an aluminum tube.
While the above-discussed fiber-reinforced drive shafts have satisfactory operating characteristics, they have been found difficult and expensive to produce on a high volume production basis.